Extraction, separation, and purification of biological molecules, such as nucleic acids and proteins, from biological samples, such as blood, blood plasma, or tissue slice samples, are fundamental, important procedures in order to obtain test substances in research on life phenomena in biological or medical field. The above procedures are used not only in the research on the life phenomena but are also used to obtain test substances in industries involved with plant variety improvement for agricultural crops, food inspection, and the like.
Regarding nucleic acid testing, in particular, polymerase chain reaction (PCR) techniques capable of DNA or RNA amplification have become common. In addition, various nucleic acid amplification techniques, such as the nucleic acid sequence-based amplification (NASBA) technique, the strand displacement amplification (SDA) technique, the self-sustained sequence replication (3SR) technique, the transcription-mediated amplification (TMA) technique, the Qβ replicase amplification technique, and the loop-mediated isothermal amplification (LAMP) technique, have been developed. Accordingly, the nucleic acid testing application range is expanding, and it is considered that demands for techniques of quicker and simpler extraction, separation and purification of nucleic acids from biological samples will keep increasing.
Phenol/chlorophorm extraction has been known as a technique for extracting, separating, and purifying a nucleic acid such as DNA or RNA from a biological sample. This technique, however, imposed serious burdens on those performing it due to the use of organic solvent or complicated procedures. In order to overcome the drawbacks described above, as a technique of extracting, separating, and purifying nucleic acids from a biological sample, a method utilizing the ability of nucleic acids to bind to silica or glass fibers in the presence of a chaotropic agent (e.g., Non Patent Literature 1) was proposed, and an automatic apparatus for implementing nucleic acid extraction was developed (e.g., Patent Literature 1 and 2).
The process of nucleic acid extraction, separation, and purification that is generally carried out with the use of an automatic apparatus is as described in (1) to (6) below.
(1) Cells contained in a biological sample are fractured with a solution containing a chaotropic agent or surfactant to elute nucleic acids in the solution. (2) Silica-coated magnetic beads (i.e., magnetic silica particles) are added to the solution and mixed therein to allow nucleic acids to absorb onto the particle surface. (3) A magnet is brought into approximate contact therewith from the outside of a reaction container, and a solution containing unnecessary substances, such as proteins, is removed with the used of a pump or other means while magnetic beads remain captured in the reaction container. (4) A wash solution is added to the reaction container, and unnecessary substances are allowed to migrate into the solution. (5) A magnet is brought into approximate contact therewith from the outside of a reaction container again, and a solution containing unnecessary substances is removed while magnetic beads remain captured in the reaction container. (6) Magnetic beads are introduced into sterilized water or low-salt buffer after the wash solution has been removed in order to elute nucleic acids from the magnetic bead surface.